It's hard to know where to start with Tentacles. So I hacked up a quick one, then made a fairly neat fan box to inflate it. Now I can try making better shaped tentacles, and I just have to clip them to the box for testing.

The main trick seems to be to not over-inflate the tentacle, then to let passing breezes drive the wiggling. This might involve (assuming the usual scrap-bin fans) putting an excess air vent in at the root end, possibly velcro-adjustable.

This tentacle is barely shaped. It started off as a shallow cone (which is bad, they need to be more cylindrical, then only tapered at the tip). The only real shape to it is a bunch of darts sewn in the sides afterwards.

A tentacle with either twist (a slipped seam) or some tailored shape would be worth trying next.